My '74 Valiant loves to stall when I have the AC on when I'm stopped at a red light or stop sign, and then I ease off the brake and onto the throttle. I've bumped up the idle quite a bit, but it still does this. I'm thinking my v-style compressor may be overcharged with refrigerant. Any other suggestions? Without the AC on, this never happens. Maybe an adjustment to the accelerator pump? Holley 1945, if that matters. Mixture too lean/rich?
stalling with AC on, coming off of idle
- Thread starter dgebhardt
- Start date
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slantsixdan
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If your A/C system is overcharged and/or there is a restriction in the A/C plumbing it will make the compressor harder to turn, but what makes you think the system might be overcharged?
Is your OSAC valve still hooked up? That's the widget on the side of the air cleaner main body with one vacuum hose running to the base of the carburetor and the other vacuum hose running to the distributor. It is a hang-on-and-pray emission control device Chrysler put on to squeak the cars past their new-vehicle emissions type-approval tests so they would be legal to put on the market. Notorious for causing or aggravating stumble/stall on attempted acceleration, and the load of the A/C compressor can easily be enough to act as a tipping point.
Run the hose directly from the carburetor to the distributor, leaving the OSAC valve out of it. Set the ignition timing to 2-1/2° BTDC (a little advanced from factory spec) and put your idle speed and other carburetor adjustments back where they're meant to be. Check for general faults (vacuum leaks, gummed-up PCV valve, cracked/missing hoses, etc).
Tune-up parts and technique suggestions are in this post, and Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.
Is your OSAC valve still hooked up? That's the widget on the side of the air cleaner main body with one vacuum hose running to the base of the carburetor and the other vacuum hose running to the distributor. It is a hang-on-and-pray emission control device Chrysler put on to squeak the cars past their new-vehicle emissions type-approval tests so they would be legal to put on the market. Notorious for causing or aggravating stumble/stall on attempted acceleration, and the load of the A/C compressor can easily be enough to act as a tipping point.
Run the hose directly from the carburetor to the distributor, leaving the OSAC valve out of it. Set the ignition timing to 2-1/2° BTDC (a little advanced from factory spec) and put your idle speed and other carburetor adjustments back where they're meant to be. Check for general faults (vacuum leaks, gummed-up PCV valve, cracked/missing hoses, etc).
Tune-up parts and technique suggestions are in this post, and Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.
No BS when slantsixdan is on the case.
OSAC has been disabled since I got her running a year ago. Dan’s posts on the slant six forum really helped for that.
All vacuum hoses were new a year ago. The only fouled piece was the plug on the charcoal canister which I replaced with a new plug.
AC was at 350psi high and 35 low. My notes from last year say that I couldn’t get it up past 160psi no matter how many cans I charged it with. That particular issue seems to have resolved itself. Today a pulled the high side down to 225 psi (it’s over 100’F here) and 30 psi low.
It still stalls with the AC on.
I’ll check the timing and air mixture next. Maybe pulls the plugs and do a visual check on them. Now that I think of it, every so often it sounds like it skips a cycle like a misfire.
All vacuum hoses were new a year ago. The only fouled piece was the plug on the charcoal canister which I replaced with a new plug.
AC was at 350psi high and 35 low. My notes from last year say that I couldn’t get it up past 160psi no matter how many cans I charged it with. That particular issue seems to have resolved itself. Today a pulled the high side down to 225 psi (it’s over 100’F here) and 30 psi low.
It still stalls with the AC on.
I’ll check the timing and air mixture next. Maybe pulls the plugs and do a visual check on them. Now that I think of it, every so often it sounds like it skips a cycle like a misfire.
I just went for a drive to get the tires rotated. Waiting at a red light, I moved the fan switch from off to low. Stalled. The AC selector switch was set to vent so the compressor should be off. Something is very much off here
slantsixdan
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Holy carp, dude. Trying to guess at charge in the system by watching the pressures is the wrong way to do it, and cramming in can after can after can trying to reach a particular gauge reading is extra super mega the wrong way to do it. Great way to break stuff and make problems that didn't have to exist and cost yourself money.
You charge by refrigerant volume or weight. You diagnose by gauge readings.
Normally, about 22 ounces will make just about any passenger car size system cool well.
From what you said in post 5, maybe the compressor is not the problem.
Look under the hood and disconnect the wire that energizes the compressor clutch.
While driving move the selector switch to different positions such as AC, Max AC. Vent, etc.
Get back to us with results.
Look under the hood and disconnect the wire that energizes the compressor clutch.
While driving move the selector switch to different positions such as AC, Max AC. Vent, etc.
Get back to us with results.
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Will do.
In the meantime, I checked the timing last night. At about 800RPM, with the vacuum advance line removed and plugged, I'm at about 14 degrees. Using a hand vacuum pump, the timing scales up to around 23 with 12 to 15 inches of vacuum applied (and the RPMs jump to roughly 1000, too). At 2300RPM, the timing is close to 35 degrees. Does this seem right?
I'll pull the plugs Friday evening and do a visual. Might as well do a compression check, too, while I have the plugs out.
Could it be that the uneven exhaust sound is due to the RV10/RV15 cam? I didn't think that it had enough overlap to create much of a lope-y sound.
Charrlie_S
Well-Known Member
That is not correct. If the system has all original components (no non original parts such as an updated condenser) the r-134a charge should be about 80 % of the R-12 charge.
I'll take your word for it. I'm just a shade-tree mechanic and I've always used the sight glass and a set of gauges to work on my AC systems. I'm always willing to learn new info, so thanks for educating me.
Charrlie_S
Well-Known Member
That information has been available for over 20 years. Just a FYI: with 134a don't rely on the site glass, and it is better to be a little undercharged, then to be overcharged.
slantsixdan
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As others have already pointed out, that info has been readily available for many years. And it popped up easy-squeezy when I googled how much R134a in an R12 system.
slantsixdan
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Times like these I want the [disagree] button back. This is not the place to go by guess and by gosh and by random number of ounces someone said on the internet.
Yeah yeah. I knew you were comin. lol
Yes, a lopey cam can cause this problem.....in any engine. It is likely the 'hotter' cam is making less tq at idle speed, & not enough tq to keep the engine running. Try increasing the initial timing 5-10* & see if that helps. Lopey idle could also be worn lobe/lifters....with same result.
Well, you know what they say about "assume", right. I for sure made an *** outta me. ;-)
I disconnected the wire going to the AC compressor and moved all of the levers to various climate settings. The blower fan came on as expected, but the compressor never came on. The car didn't stall. I plugged in the compressor wire and the compressor kicked in. The car did not stall. I moved the car out of the driveway and shifting from R to D caused a stall.
I checked all of the vacuum lines. I found another cap that was cracked and replaced it. The PCV hose was very loose, so I added hose clamps to either end.
Using my timing light and vacuum gauge (manifold vacuum), I tried to adjust the timing to maximize the vacuum and until the engine sounded the best. I took it for a spin and it stalled in the driveway. I pulled the valve cover and checked the valve lash, adjusting to 0.12 for the exhaust and 0.09 for the intake (recommended by the cam mfr). I pulled the #1 plug and it looked good (grey brown) and the gap was 0.035. I found that the plug wire for #1 was pushed back into the boot pretty far. I readjusted the wire and reinstalled the plug and wire. I started tinkering with the timing again. I adjusted the AFR mixture screw to slightly rich. I can get the idle vacuum up to nearly 18", but kicking on the AC drops it to 14" and then going into R or D drops it even more (following the RPMs). It was getting late and I was hot, so I upped the idle and drove it around the block. No stalling. I'm at the edge of the adjustment slot in the dizzy, so I'll need to loosen the bottom bolt and readjust the slotted plate (I hope there is room for it to adjust). Idle timing at roughly 900-1000 RPM is roughly 20'.
What should I do next? I'd love to get the idle down a bit, since the car wants to lurch pretty hard when I move it into gear. And it still has a very occasional miss. Continue with the ignition timing? Smaller spark plug gaps? Move plugs and wires around? Compression test? Leakdown test? Spray some sort of aerosol and check for vacuum leaks?
I checked all of the vacuum lines. I found another cap that was cracked and replaced it. The PCV hose was very loose, so I added hose clamps to either end.
Using my timing light and vacuum gauge (manifold vacuum), I tried to adjust the timing to maximize the vacuum and until the engine sounded the best. I took it for a spin and it stalled in the driveway. I pulled the valve cover and checked the valve lash, adjusting to 0.12 for the exhaust and 0.09 for the intake (recommended by the cam mfr). I pulled the #1 plug and it looked good (grey brown) and the gap was 0.035. I found that the plug wire for #1 was pushed back into the boot pretty far. I readjusted the wire and reinstalled the plug and wire. I started tinkering with the timing again. I adjusted the AFR mixture screw to slightly rich. I can get the idle vacuum up to nearly 18", but kicking on the AC drops it to 14" and then going into R or D drops it even more (following the RPMs). It was getting late and I was hot, so I upped the idle and drove it around the block. No stalling. I'm at the edge of the adjustment slot in the dizzy, so I'll need to loosen the bottom bolt and readjust the slotted plate (I hope there is room for it to adjust). Idle timing at roughly 900-1000 RPM is roughly 20'.
What should I do next? I'd love to get the idle down a bit, since the car wants to lurch pretty hard when I move it into gear. And it still has a very occasional miss. Continue with the ignition timing? Smaller spark plug gaps? Move plugs and wires around? Compression test? Leakdown test? Spray some sort of aerosol and check for vacuum leaks?
Question about vacuum hoses.
You should have a vacuum fitting that is screwed into the intake manifold.
How many nipples are on the fitting and where do the hose or hoses go from the fitting.
Didn't the 1974 models have vacuum hoses connected to the egr valve,temp sensor on radiator, vacuum amplifier, etc.
You should have a vacuum fitting that is screwed into the intake manifold.
How many nipples are on the fitting and where do the hose or hoses go from the fitting.
Didn't the 1974 models have vacuum hoses connected to the egr valve,temp sensor on radiator, vacuum amplifier, etc.
The manifold vacuum nipple has 2 outlets, one smaller than the other. I'd have to check to be 100% sure, but I believe that one goes to the HVAC vacuum reservoir and one goes to the vacuum amplifier.
Here's a way to test for any vacuum leaks from those hoses.
Clamp shut the hoses coming off the manifold fitting or plug the hoses and use rubber caps on the fittings.
Then drive the car with AC on. Air will came out of the wrong dash outlets but that won't matter.
See if it still stalls.
This would test for any leaks associated with those hoses and components.
In today's repair shops a smoke machine would be used.
Clamp shut the hoses coming off the manifold fitting or plug the hoses and use rubber caps on the fittings.
Then drive the car with AC on. Air will came out of the wrong dash outlets but that won't matter.
See if it still stalls.
This would test for any leaks associated with those hoses and components.
In today's repair shops a smoke machine would be used.
I’ll give it a try.
I have a homemade smoke maker. How do I use it to test the vac system?
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